Method of expanding a tubular element in a wellbore

ABSTRACT

A method is provided of radially expanding a tubular element ( 4 ) extending into a wellbore formed in an earth formation, comprising the steps of arranging an expander ( 8 ) in the tubular element ( 4 ), the expander ( 8 ) being operable to exert a radial force to the inner surface of the tubular element ( 4 ), and radially expanding the tubular element by pressurising the interior of the tubular element ( 4 ) and simultaneously operating the expander ( 8 ) to exert said radial force to the inner surface of the tubular element. The expander ( 8 ) is operated to exert said radial force to the inner surface of the tubular element ( 4 ) independently from pressurising the interior of the tubular element.

The present invention relates to a method of radially expanding a tubular element extending into a wellbore formed in an earth formation, whereby an expander located in the tubular element, is operable to exert a radial force to the inner surface of the tubular element.

Wellbores for the production of hydrocarbon fluid are conventionally provided with one or more casings to provide stability to the wellbore wall, and/or to provide zonal isolation between different earth formation layers. Generally, several casings are set at different depth intervals in a nested arrangement whereby the diameter of each subsequent casing is smaller than the diameter of the previous casing in order to allow lowering of the casing through the previous casing.

Recently it has become practice to radially expand tubular elements in the wellbore, for example as a clad against an existing casing section. Also, it has been proposed to construct a monodiameter well by radially expanding each subsequent casing to substantially the same diameter as the previous casing. It is thus achieved that the available diameter of the wellbore is kept substantially constant along (a portion of) its depth, as opposed to the conventional nested arrangement whereby the available diameter decreases stepwise with each subsequent casing. The monodiameter concept is particularly of interest for very deep wellbores or extended reach wellbores. To expand the tubular element, an expander of diameter substantially equal to the required expanded inner diameter, is pumped, pushed or pulled, sometimes in combination with rotation, through the tubular element.

In one such method the expander is pumped through the tubular element whereby the interior of the expanded portion of the tubular element is pressurised to a maximum pressure at which the expander starts moving through the tubular element. However it has been experienced that the required expansion forces exerted by the expander to the tubular element can be very high, thus potentially leading to damage to the expander and/or the inner surface of the tubular element.

It is therefore an object of the invention to provide an improved method of expanding a tubular element in a wellbore, which overcomes the drawbacks of the prior art.

In accordance with the invention there is provided a method of radially expanding a tubular element extending into a wellbore formed in an earth formation, comprising the steps of:

arranging an expander in the tubular element, the expander being operable to exert a radial force to the inner surface of the tubular element;

radially expanding the tubular element by pressurising the interior of the tubular element and simultaneously operating the expander to exert said radial force to the inner surface of the tubular element,

wherein the expander is operated to exert said radial force to the inner surface of the tubular element independently from pressurising the interior of the tubular element.

By operating the expander independently from pressurising the interior of the tubular element, it is achieved that the interior of the tubular element can be pressurised to a significantly higher pressure so that the required expansion forces exerted by the expander to the tubular element can be relatively low.

Suitably the tubular element includes an expanded portion and an unexpanded portion, whereby the interior of the tubular element is pressurised both in the expanded portion and the unexpanded portion. For example, the whole interior of the tubular element can be pressurised.

The invention will be explained hereinafter in more detail by way of example, with reference to the accompanying drawings in which:

FIG. 1 schematically shows a first embodiment of a wellbore provided with a casing expanded according to the method of the invention; and

FIG. 2 schematically shows a second embodiment of a wellbore provided with a liner expanded according to the method of the invention.

In the drawings and the detailed description below, like reference numerals relate to like components. Furthermore, it is to be understood that the terms “below”, “above”, “upward” and “downward” refer to wellbore depths measured along the longitudinal axis of the wellbore and relative to surface.

Referring to FIG. 1 there is shown a wellbore 1 for the production of oil or gas from an earth formation 2. An expandable casing 4 extends from a wellhead 6 at surface to near the lower end of the wellbore 1, whereby the casing 4 is sealingly connected to the wellhead 6. An expander 8 for radially expanding the casing 4, is positioned in the casing 4 whereby an expanded portion 10 of the casing 4 extends below the expander 8, and an unexpanded portion 12 of the casing 4 extends above the expander 8. The lower end of the expanded casing portion 10 is closed by means of a packer 13.

The expander 8 tapers in upward direction from a relatively large diameter corresponding to the inner diameter of the expanded casing 4, to a relatively small diameter corresponding to the inner diameter of the unexpanded casing 4. There are no provisions to seal the outer surface of the expander 8 to the inner surface of the casing 4, so that pressurised fluid can flow between the expander 8 and the casing 4.

The expander 8 is provided with a through-bore 14 providing fluid communication between the interior of the unexpanded casing portion 12 and the interior of the expanded casing portion 10. The expander 8 is connected to a wireline 16 extending through the unexpanded casing portion 12 and the wellhead 6, to a winch 18 at surface. The wireline 16 passes through a through-bore 19 provided in the wellhead 6 in a sealing manner so that the wireline 16 can be axially moved through the through-bore 19 while fluid is prevented from passing through the through-bore 19. Further, a fluid pump 20 is provided at surface for pumping fluid, via a conduit 22 and the wellhead 6, into the casing 4.

Referring to FIG. 2 there is shown a wellbore 1 for the production of oil or gas from an earth formation 2. A casing 24 extends from surface to a depth at a selected distance from the wellbore bottom, the casing 24 being fixed in the wellbore by a layer of cement (not shown). Further, an expandable liner 26 extends in the wellbore below the casing 24, whereby an upper end portion of the liner 26 extends into the casing 24. The liner 26 is suspended on a drill pipe 28, with a side entry sub 30 interconnecting the liner 26 and the drill pipe 30. The drill pipe 28 extends to a conventional drilling rig (not shown) at surface, and is connected to a fluid pump (not shown) for pumping fluid via the drill pipe 28 into the liner 26.

An expander 32 for radially expanding the liner 26 is positioned in the liner 26, whereby an expanded portion 34 of the liner 26 extends below the expander 32, and an unexpanded portion 36 of the liner 26 extends above the expander 32. The lower end of the expanded liner portion 34 is closed by means of a packer 37. The expander 32 tapers in upward direction from a relatively large diameter corresponding to the inner diameter of the expanded liner portion 34, to a relatively small diameter corresponding to the inner diameter of the unexpanded liner portion 34. There are no provisions to seal the outer surface of the expander 32 to the inner surface of the liner 26, so that pressurised fluid can flow between the expander 32 and the liner 26. To ensure free flow of fluid between the unexpanded liner portion 36 and the expanded liner portion 34, the expander is optionally provided with a through-bore (not shown) similar to the through-bore 14 of the FIG. 1 embodiment.

The expander 32 is at its lower end provided with an extender 40 comprising a lower leg 42 and an upper leg 43, the legs being axially movable relative to each other. The lower leg 42 is provided with a lower anchor 44, and the upper leg 43 is provided with an upper anchor 45. Each anchor 44, 45 is operable between a radially retracted position in which the anchor 44, 45 is free from the inner surface of the liner 26, and a radially extended position in which the anchor 44, 45 is anchored to the inner surface of the liner 26. The extender 40 is operable between an axially retracted position in which the anchors 43, 45 are close to each other, and an axially extended position in which the anchors 43, 45 are remote from each other. The extender 40 and the anchors 43, 45 are electrically operated, whereby electric power is provided to the extender 40 and the anchors 43, 45 through an electric power cable 46 extending from surface along the drill pipe 28 and passing, via an opening (not shown) in the side entry sub 30, into the liner 26. The power cable 46 extends in a loop 48 below the extender 40 to allow for axial displacement of the expansion assembly relative to the side entry sub 30.

During normal operation of the embodiment shown in FIG. 1, the fluid pump 20 is operated to pump fluid, via the conduit 22 and the wellhead 6, into the interior of the casing 4 at the upper end thereof. The packer 13 prevents outflow of fluid from the lower end of the casing 4. As a result of the pumping operation, the fluid pressure in the casing 4 increases whereby the increase of fluid pressure in the expanded (lower) casing portion 10 equals the increase of fluid pressure in the unexpanded (upper) casing portion 12 by virtue of the through-bore 14 of the expander 8. Also, the fluid pressure between the outer surface of the expander 8 and the inner surface of the casing 4 increases equally. Pumping of fluid into the casing 4 is continued until the fluid pressure in the casing 4 is about 90% of the burst pressure of the casing 4. It is to be understood that the burst pressure of the casing is the internal fluid pressure at which the casing 4 deforms in an uncontrolled manner, leading to rupture of the casing. For given casing characteristics, such as diameter, wall thickness, steel properties, and roundness, the burst pressure can be determined in a straightforward manner, either by calculation or by testing. Also, for most casings generally used the burst pressure is known or can be obtained from the manufacturer.

Upon the fluid pressure in the casing 4 reaching about 90% of the casing burst pressure, the winch 20 is operated to pull the expander 8 upwardly by means of the wireline 16. In view of the high fluid pressure in the casing 4, the force required to pull the expander 8 upwardly through the casing, and thereby to radially expand the casing 4, is relatively low. The pressurised fluid between the outer surface of the expander 8 and the inner surface of the casing delivers a major amount of the energy required to radially expand the casing 4. Therefore the expander 8 only needs to exert a moderate radial force to the inner surface of the casing 4 to expand the casing. Since the internal volume of the casing 4 increases during the expansion process, it is necessary to continue pumping fluid into the casing 4 during the expansion process in order to keep the fluid pressure at about 90% of the burst pressure. The expansion process proceeds until the expander arrives at the upper end of the casing 4, whereafter the expander 8 is retrieved from the wellbore 1.

During normal operation of the embodiment shown in FIG. 2 the fluid pump at surface is operated to pump fluid, via the drill pipe 28 and the side entry sub 30, into the interior of the liner 26. The packer 37 prevents outflow of fluid from the lower end of the liner 26. As a result of the pumping operation, the fluid pressure in the liner 26 increases whereby the fluid pressure increase in the expanded (lower) riser portion 34 equals the fluid pressure increase in the unexpanded (upper) liner portion 36. Also, the fluid pressure between the outer surface of the expander 32 and the inner surface of the liner 26 increases equally. Pumping of fluid into the liner 26 is continued until the fluid pressure in the liner 26 is about 90% of the burst pressure of the liner 26. The burst pressure is the internal fluid pressure at which the liner 26 deforms in an uncontrolled manner, eventually leading to rupture of the liner 26. Similarly to the burst pressure for casing, the burst pressure for liner can be determined in a straightforward manner, either by calculation or by testing. Alternatively the burst pressure can be obtained from the manufacturer.

Upon the fluid pressure in the liner 26 reaching about 90% of the liner burst pressure, with the extender 40 in the retracted position, the lower anchor 44 is operated to move to its radially extended position so as to anchor the lower leg 42 to the inner surface of the liner 26. Then the extender 40 is operated to move to its axially extended position so as to move the expander 32 one stroke upwardly through the liner 26 and to further expand the liner 26. In view of the high fluid pressure in the liner 26, the force required to move the expander 32 upwardly through the liner 26, and thereby to radially expand the liner, is relatively low. The pressurised fluid between the outer surface of the expander and the inner surface of the liner delivers a major amount of the energy required to radially expand the liner 26. Therefore the expander 26 only needs to exert a moderate radial force to the inner surface of the liner 26 to expand the liner. Since the internal volume of the liner 26 increases during the expansion process, it is necessary to continue pumping fluid into the liner 26 during the expansion process in order to keep the fluid pressure at about 90% of the burst pressure. Upon the extender 40 arriving at the end of its stroke, the upper anchor 45 is moved to its radially extended position so as to anchor the upper leg 43 to the inner surface of the liner 26, and the lower anchor 44 is moved to its radially retracted position. The extender 40 is then moved to its axially retracted position whereby the lower leg 42 and lower anchor 44 move upwardly through the liner 26. The expansion process described above is then repeated so as to move the expander 32 a further stroke upwardly, etc. During the final stage of the expansion process, the upper end portion of the liner 26 is expanded against the casing 24 whereby the liner becomes firmly fixed to the casing 24. After the liner 26 has been completely expanded, the expander 32, the extender 40, the power cable 46, the side entry sub 30 and the drill pipe 28 are retrieved from the wellbore 1.

Instead of using the electrically operated anchors described hereinbefore, self-activating anchors can be used. For example, an anchor can be used which anchors itself against the inner surface of the liner upon application of a downward force to the anchor, and which releases itself from the liner upon application of an upward force to the anchor. Such principle is similar to the principle of a conventional ball grabber.

Furthermore, instead of powering the extender and/or anchors electrically, the extender and/or anchors can be hydraulically powered using, for example, a coiled tubing. Also, a combination of electric and hydraulic powering can be applied.

Instead of pulling the expander through the tubular element in upward direction, the expander can be operated to exert said radially outward force to the inner surface of the tubular element by allowing the expander to move through the tubular element by gravitational force. In order to enhance the gravitational force acting on the expander, the expander is suitably provided with additional weight means or with propelling means such as the extender described hereinbefore. 

1. A method of radially expanding a tubular element extending into a wellbore formed in an earth formation, comprising the steps of: arranging an expander in the tubular element, the expander being operable to exert a radial force to the inner surface of the tubular element; radially expanding the tubular element by pressurising the interior of the tubular element and simultaneously operating the expander to exert said radial force to the inner surface of the tubular element, wherein the expander is operated to exert said radial force to the inner surface of the tubular element independently from pressurising the interior of the tubular element.
 2. The method of claim 1, wherein the tubular element includes an expanded portion and an unexpanded portion, and wherein the interior of the tubular element is pressurised both in the expanded portion and the unexpanded portion.
 3. The method of claim 2, wherein substantially the whole interior of the tubular element is pressurised.
 4. The method of claim 1, wherein the interior of the tubular element is pressurised by pumping a fluid into the tubular element.
 5. The method of claim 4, wherein the tubular element has an upper end located substantially at surface, and wherein said fluid is pumped into the tubular element at or near said upper end of the tubular element.
 6. The method of claim 1, wherein the interior of the tubular element is pressurised to a pressure of between 80%-95% of the burst pressure of the tubular element.
 7. The method of claim 6, wherein the interior of the tubular element is pressurised to a pressure of about 90% of the burst pressure of the tubular element.
 8. The method of claim 1, wherein the expander has a largest diameter larger than the inner diameter of the unexpanded tubular element, and wherein the expander is operated to exert said radially outward force to the inner surface of the tubular element by moving the expander through the tubular element.
 9. The method of claim 8, wherein the expander is moved through the tubular element by pulling the expander through the tubular element by means of a pulling string.
 10. The method of claim 1, wherein the expander is movable between a radially retracted mode and a radially expanded mode, and wherein the expander is operated to exert said radial force to the inner surface of the tubular element by moving the expander from said radially retracted mode to said radially expanded mode.
 11. The method of claim 1, wherein the tubular element is a wellbore casing or a wellbore liner.
 12. (canceled) 